The use of ultrasonic test equipment to inspect workpieces is well known, see for example the U.S. Pat. No. 3,828,609 to Furon et al. Typically, a workpiece is mounted on a turntable inside a tank, which is filled with a liquid such as water. An ultrasonic probe is mounted so that it will direct ultrasonic energy onto the workpiece. The typical ultrasonic testing system, such as may be used to inspect aircraft engine parts, the turntable is rotated while submerged in a water filled tank and the ultrasonic probe moved, in a scanning plane, relative to the workpiece. The turntable drive components as well as supports and adjustments needed to orient the turntable are all located inside the tank.
Such prior art ultrasonic testing system has several undesirable features. For example, the turntable has to be elevated above the bottom of the tank (thus requiring a large and deep tank) to provide adequate room for controls and linkages needed to adjust the orientation of the turntable and provide rotational drive. Angular adjustments to the turntable are difficult to make in a deep tank and frequently require that the tank first be drained. As a result, accurate parallel alignment between the plane of rotation of the turntable with respect to the scanning plane of the ultrasonic probe is difficult to achieve. In addition, the water environment inside the tank is not compatible with the components used to control and drive the turntable so that bearings and similar components may quickly deteriorate, thus requiring more frequent replacement and maintenance.